Tips On Tubing - Tube Bending 101

Whether it’s working in the professional rod building world or as a hobbyist, to stay employed and/or successful at completing personal projects, you need to be capable in as many skills as you can. Fabrication and welding skills are at the top of the list, but there are a heck of a lot of others that’ll need to be mastered as well.

One skill that’s important is the successful shaping and bending of the various diameters of tubing that go into completing a project. Here we’ll take a look at some examples of brake and fuel lines. These are all made from various sized tubing bent into a flowing pattern of precisely placed twists and turns. Knowing how to properly plan, bend, flare and secure the tubing is a skill that all us wrench turners will benefit from. It’s a skill that doesn’t take an extremely long time to master and the following should help you hone these useful skills.

The key to doing it right the first time is to bend a wire template first. For this purpose, lengths of welding wire work well. If more length is needed, tape another piece to the first wire. You’ll find that it’s a lot easier to change the bends in the wire templates than to change the bent tube.

Flaring is a required skill as well. For regular steel lines there are double flares (45-degree). Stainless steel lines use a single flare (37-degree). Although you can single flare regular steel line and use AN style fittings on them you can’t, however, double flare stainless lines. When single flaring a stainless steel line, you need to be very mindful of not cracking the tube end.

The trick with the double flare kits is to always file a 45-degree angle on the outside end of the tube before you flare it. If you don’t do it on the 3⁄16-inch steel brake line, you may snap off the centering pin of the flare die as the tube rolls over into itself for the first step of the flare.

Just like any other fabrication step, bending tubing should start with a plan. Brake and fuel lines will have different fittings that are needed. How they are run on the framerails will depend in some cases where exhaust has been or is going to be run. Lay out your plan on paper and list the various fittings you’ll need. Unions are used to join separate sections of tubing and are handy for splitting a long running section of line in two for easier installation.

There are various sized steel nuts for the 3⁄16-inch brake lines available so you don’t need reducer fittings in most cases. The steel lines most commonly used are 60-inch-long pieces from the local parts store. They come with a short and a long flare nut on these pre-flared lines.

Before you start bending any lines, always have all the components you’re running tubing from or to mounted in their final resting places. In brake systems for example, the mounting tabs for the flex hoses should be located and attached to the frame near where the wheel cylinders / calipers are located. The master cylinder and proportioning valve (if applicable) should be mounted also. The residual check valves needed should be on hand (if not provided for in a metering/proportioning valve), and you’ll need a T-fitting for a brake light pressure switch if you’ve decided not to use a lever-actuated mechanical switch.

Some of the underhood tubing can be bent and installed before engine installation. The vacuum tube for the power brake booster (if mounted to the vehicle frame rather than the firewall) and the transmission is a lot easier to do with the engine and trans on the ground. It will run from a fitting in the intake manifold behind the carb down the back of the engine, following the top of the bellhousing and back to where the tailshaft housing cover bolts on. From here you can use a T to run a rubber hose to the brake booster and, if needed, to the vacuum shift modulator.

Utilizing proper benders, flaring tools, patience and practice, anyone should be able to master this skill. Just keep in mind that there’s a learning curve here; don’t expect your first couple of lines to be perfect. But once mastered, it’s a great skill to have mastered. Well-formed and located tubing is an important detail in a quality build so follow along with the pictures below for one example of how to bend up fuel and vacuum lines for a small-block Chevy.

01 Here’s a stock little 350 Chevy with the usual bolt-ons. Here we’ll try to give you some pointers and tips so you can plumb any system you might need.

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02 First of all, no matter what a specific line will be used for, it’s always a good idea to use a piece of wire to make a pattern. With practice you can achieve the desired result the first time this way.

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03 As an example, this photo shows a wire pattern being used to determine the shape of a fuel line that’ll snake through an A/C mount and up toward the intake manifold and carburetor.

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04 The tubing normally used for fuel supply lines is standard 3⁄8-inch steel line. It can be purchased in 60-inch lengths. It usually takes three of them to do a complete fuel system. Using our wire pattern as a guide, we make a reference mark on the tube. The trick to getting your bend in the right spot is to always have your reference mark line up with the bend degree when you finish the bend.

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05 With the first bend made to exit the fuel pump, the next will give the line its upward direction. Here, a reference mark lines up on the 45-degree mark on the bender face.

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06 With the bend made to pass under and through the A/C bracket we made the last two bends to get the line up onto the intake manifold.

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07 The first test fit looks pretty good, though sometimes even with the help of a pattern, small adjustments may be required. This shows how the line snakes its way under the A/C compressor and behind the thermostat housing.

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08 With the fuel supply line bent into the correct shape the next step will be flaring the ends of the tubing. With the line in the flaring tool clamp, line up the top of the tube to the first ridge on the double flare 3⁄8-inch die. Notice that the edge of the tube has been beveled. This is key to a successful flare. When the tool is compressed onto the tube, it rolls the tube inward, giving the first step in a double flare. If you don’t bevel the edge of smaller 3⁄16-inch brake size tubing, there’s a good chance you’ll break off the die pin … been there, done that.

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09 After you compress the die down all the way this is what it should look like.

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10 Next, remove the die and then use the point of the flaring tool into the tube and tighten it down. Screw it down until it stops and give another quarter turn. This takes a bit of practice because if you go too tight you may split the tube.

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11 Here we have a finished double flare. Always give the flare a check and make sure its seat is smooth and there are no cracks. Those cracks will cause leaks that will drive you crazy.

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12 Here is the finished fuel line example. It fits well and sure looks much more professional than a long piece of rubber fuel hose.

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13 Here is another example of successful tube shaping. This is the portion of line that exits the fuel tank and is routed up along the C-section in the frame, along the boxing plate, and then along the framerail. It follows the framerail all the way forward to the fuel pump inlet. The next step here would be to mount the line to the frame with the use of a few strategically placed line clamps.

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14, 15 These two images are good examples of the shape and routing of some forward sections of brake lines. As we said earlier, with some time, a bit of practice, the correct tools, and some wire templates anyone can learn to fabricate fuel, brake, and vacuum lines like a pro.